Citation

Abstract

LixNi0.5Mn0.5O2 and LixNi1/3Mn1/3Co1/3O2 are cathode materials in Li-ion batteries. The changes in their electronic structure during charging/discharging processes were studied by using electron energy loss spectrometry (EELS) in a transmission electron microscope (TEM) and first-principles calculations. Significant growth was observed at O K-edge upon the removal of lithium, indicating a depletion of O 2p electrons. Only small changes were observed on Ni absorption edges. Our results indicate that the widely believed Ni2+ -> Ni4+ oxidation does not occur during delithiation, and O is mainly responsible for the charge compensation in these materials. Following similar procedure, the olivine phases of LixFePO4 were studied. It was found that about half electron was donated by Fe atoms during delithiation, while the rest of the charge was contributed by O atoms. We also studied the bonding in Mg2Si. The Mg-Si bond was found to be very ionic. An ionicity of 74% was found via Bader analysis.